Publications by authors named "Mozart N Ramos"

10 Publications

  • Page 1 of 1

Thiosemicarbazones as Aedes aegypti larvicidal.

Eur J Med Chem 2015 Jul 28;100:162-75. Epub 2015 May 28.

Quantum Theory Project, University of Florida, 2234 New Physics Building, Gainesville, PO Box 118435, Florida, USA.

A set of aryl- and phenoxymethyl-(thio)semicarbazones were synthetized, characterized and biologically evaluated against the larvae of Aedes aegypti (A. aegypti), the vector responsible for diseases like Dengue and Yellow Fever. (Q)SAR studies were useful for predicting the activities of the compounds not included to create the QSAR model as well as to predict the features of a new compound with improved activity. Docking studies corroborated experimental evidence of AeSCP-2 as a potential target able to explain the larvicidal properties of its compounds. The trend observed between the in silico Docking scores and the in vitro pLC50 (equals -log LC50, at molar concentration) data indicated that the highest larvicidal compounds, or the compounds with the highest values for pLC50, are usually those with the higher docking scores (i.e., greater in silico affinity for the AeSCP-2 target). Determination of cytotoxicity for these compounds in mammal cells demonstrated that the top larvicide compounds are non-toxic.
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http://dx.doi.org/10.1016/j.ejmech.2015.04.061DOI Listing
July 2015

Hydrogen bonds determine the structures of the ternary heterocyclic complexes C₂H₄O···2HF, C₂H₅N···2HF and C₂H₄S···2HF: density functional theory and topological calculations.

J Mol Model 2011 Nov 8;17(11):2847-62. Epub 2011 Feb 8.

Departamento de Química, Universidade Federal da Paraíba, 58036-300 João Pessoa, PB, Brazil.

A theoretical study of structural, electronic, topological and vibrational parameters of the ternary hydrogen-bonded complexes C(2)H(4)O···2HF, C(2)H(5)N···2HF and C(2)H(4)S···2HF is presented here. Different from binary systems with a single proton donor, the tricomplexes have the property of forming multiple hydrogen bonds, which are analyzed from a structural and vibrational point of view, but verified only by means of the quantum theory of atoms in molecules (QTAIM). As traditionally done in the hydrogen bond theory, the charge transfer between proton donors and acceptors was computed using the CHELPG calculations, which also revealed agreement with dipole moment variation and a cooperative effect on the tricomplexes. Furthermore, redshift events on proton donor bonds were satisfactorily identified, although, in this case, an absence of experimental data led to the use of a theoretical argument to interpret these spectroscopic shifts. It was therefore the use of the QTAIM parameters that enabled all intermolecular vibrational modes to be validated. The most stable tricomplex in terms of energy was identified via the strength of the hydrogen bonds, which were modeled as directional and bifurcated.
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http://dx.doi.org/10.1007/s00894-011-0969-8DOI Listing
November 2011

A chemometrical study of intermolecular properties of hydrogen-bonded complexes formed by C2H4O...HX and C2H5N...HX with X = F, CN, NC, and CCH.

J Mol Model 2009 Apr 13;15(4):421-32. Epub 2008 Dec 13.

Departamento de Química, Universidade Federal da Paraíba, 58036-300, João Pessoa, PB, Brazil.

We presents a chemometrical study of the intermolecular properties of the C(2)H(4)O...HX and C(2)H(5)N... HX hydrogen-bonded complexes with X = F, CN, NC, and CCH. Through the MP2 perturbation theory and B3LYP hybrid functional, as well as modifications on 6-31ijGk basis sets with i = triple-zeta, j = diffuse and k = polarization functions, systematic tendencies in the R((n...HX)) hydrogen bond distances and upsilon((n...HX)) stretch frequencies were determined by the hierarchical cluster analysis, two level factorial designs and principal component analysis. Based on well-fitted math models, not only because polarization functions provide a great variance on statistical analysis, but this basis set reproduces more efficiently the available experimental results. Moreover, independent of whether the quality on basis set is increased, the effects yielded by both DFT and MP2 were not considered important in the statistical analysis.
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http://dx.doi.org/10.1007/s00894-008-0422-9DOI Listing
April 2009

The molecular properties of heterocyclic and homocyclic hydrogen-bonded complexes evaluated by DFT calculations and AIM densities.

J Mol Model 2009 Feb 27;15(2):123-31. Epub 2008 Nov 27.

Departamento de Química, Universidade Federal da Paraíba, 58036-300 João Pessoa, PB, Brazil.

This theoretical study presents a comparative analysis of the molecular properties of heterocyclic (C2H4O...HF and C2H5...HF) and homocyclic (C3H6...HF) hydrogen-bonded complexes. Initially, the equilibrium geometries of these complexes were analyzed in detail at the B3LYP/6-311++G(d,p) level of theory. Subsequently, the interaction energies and polarizabilities were also evaluated, as well as the infrared stretch frequencies and absorption intensities. In addition, by combining intermolecular criteria and charge density concepts, calculations of Bader's theory of atoms in molecules were used to determine the maxima and minima for electron density in order to measure the strength of the n...H and ppi...H hydrogen bonds. Finally, the possibility of an F...H(alpha) secondary interaction between the fluoride (F) of hydrogen fluoride and the axial hydrogen atoms (H(alpha)) of the C2H4O and C2H5N heterocyclic rings was explored.
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http://dx.doi.org/10.1007/s00894-008-0380-2DOI Listing
February 2009

CASSCF and multireference CI with singles and doubles study of low-lying valence and Rydberg states of 2H-tetrazole.

J Comput Chem 2009 May;30(7):1075-81

Departamento de Química, CCEN, Universidade Federal da Paraíba, João Pessoa/PB 58059-900 Brazil.

Complete active space self-consistent field (CASSCF) and multireference CI with singles and doubles (MR-CISD) calculations [including extensivity corrections, at MR-CISD+Q and multireference averaged quadratic coupled cluster (MR-AQCC) levels] have been performed to characterize the low-lying valence and the Rydberg states of 2H-tetrazole. The highest level results (MR-AQCC/d'-aug'-cc-pVDZ) indicate the following ordering of the valence singlet excited states: S(1) (n-pi*), 6.06 eV; S(2) (n-pi*), 6.55 eV; S(3) (pi-pi*), 6.55 eV. The MR-CISD+Q/d'-aug'-cc-pVDZ results indicate the same ordering, but at slight higher energies: 6.16, 6.68, and 6.69 eV, respectively. According to our MR-CISD+Q/d'-aug'-cc-pVDZ results, the next two states are Rydberg states, at 7.69 eV (pi-3s) and 7.89 eV (n-3s). The calculated energies of these two states, as well as their proximity, are consistent with the conclusion reached by Palmer and Beveridge (Chem Phys 1987, 111, 249) that the first band of the photoelectron spectrum of 2H-tetrazole is likely to be associated to the first two ionizations processes (of pi and N lone pair electrons), at energies close to 11.3 eV.
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http://dx.doi.org/10.1002/jcc.21133DOI Listing
May 2009

The electronic structure of the C2H4O...2HF tri-molecular heterocyclic hydrogen-bonded complex: a theoretical study.

J Mol Model 2008 Oct 15;14(10):949-55. Epub 2008 Jul 15.

Departamento de Química, Universidade Federal da Paraíba, 58036-300, João Pessoa, PB, Brazil.

The geometries of three isomers of the C2H4O...2HF tri-molecular heterocyclic hydrogen-bonded complex were examined through B3LYP/aug-cc-pVDZ calculations. Analysis of structural parameters, determination of CHELPG (charge electrostatic potential grid) intermolecular charge transfer, interpretation of infrared stretching modes, and Bader's atoms in molecules (AIM) theory calculations was carried out in order to characterize the hydrogen bonds in each isomer of the C2H4O...2HF complex. The most stable structure was determined through the identification of hydrogen bonds between C2H4O and HF, (O...H), as well as in the hydrofluoric acid dimer, (HF(D-R)...HF(D)). However, the existence of a tertiary interaction (F(lambda)...H(alpha)) between the fluoride of the second hydrofluoric acid and the axial hydrogen atoms of C2H4O was decisive in the identification of the preferred configuration of the C2H4O...2HF system.
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http://dx.doi.org/10.1007/s00894-008-0337-5DOI Listing
October 2008

Theoretical calculations of the molecular properties of maleimide and its dimer.

Spectrochim Acta A Mol Biomol Spectrosc 2008 Nov 17;71(1):5-9. Epub 2007 Nov 17.

Departamento de Química Fundamental, Universidade Federal de Pernambuco, 50740-540 Recife PE, Brazil.

B3LYP theoretical calculations with 6-31++G(d,p) basis set have been performed to study the infrared spectrum of maleimide and its dimer. Our calculations have shown that the dimer formation leads to a binding energy of 44.0 kJ mol(-1) involving two intermolecular hydrogen bonds between the amide hydrogen and a carbonyl group of two neighboring maleimides. This value is essentially due to the electrostatic interaction term. Our calculations have also revealed the vibrational changes, in terms of frequencies and IR intensities, after dimer formation. The most affected modes are associated with the N-H stretching and in-plane bending bands. This behavior can be adequately interpreted by the hydrogen atomic charge and N-H charge-flux based on the modified charge-charge flux-overlap model for infrared intensities. The B3LYP frequency shifts are in very good agreement with the experimental ones.
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http://dx.doi.org/10.1016/j.saa.2007.11.002DOI Listing
November 2008

Dissociation of ground and nsigma* states of CF3Cl using multireference configuration interaction with singles and doubles and with multireference average quadratic coupled cluster extensivity corrections.

J Chem Phys 2007 Oct;127(16):164320

Departamento de Química, CCEN, Universidade Federal da Paraíba, João Pessoa, Paraíba 58036-300 Brazil.

Extended complete active space self-consistent field (CASSCF), multireference configuration interaction with singles and doubles (MR-CISD), and multireference average quadratic coupled cluster (MR-AQCC) calculations have been performed on the ground (S(0)) and first excited (nsigma(*),S(1)) states of the CF(3)Cl molecule. Full geometry optimizations have been carried out for S(0) as well as "relaxed" potential energy calculations for both states, along the C-Cl bond distance. Vertical excitation energies (DeltaE(vertical)), dissociation energies (DeltaE(diss)), dissociation enthalpies (DeltaH(diss)), and the oscillator strength (f) have also been computed. Basis set effects, basis set superposition error (BSSE), and spin-orbit and size-extensivity corrections have also been considered. The general agreement between theoretical and available experimental results is very good. The best results for the equilibrium geometrical parameters of S(0) (at MR-AQCCaug-cc-pVTZ+d level) are 1.762 and 1.323 A, for the C-Cl and C-F bond distances, respectively, while the corresponding experimental values are 1.751 and 1.328 A. The [angle](ClCF) and [angle](FCF) bond angles are in excellent agreement with the corresponding experimental values (110.3 degrees and 108.6 degrees ). The best calculated values for DeltaE(vertical), DeltaH(diss), and f are 7.63 eV [at the MR-AQCCaug-cc-pV(T+d)Z level], 3.59 eV[MR-AQCCaug-cc-pV(T+d)Z level+spin-orbit and BSSE corrections], and 2.74x10(-3) (MR-CISD/cc-pVTZ), in comparison with the corresponding experimental values of 7.7+/-0.1 eV, 3.68 eV, and 3.12 x 10(-3)+/-2.50 x 10(-4). The results concerning the potential energy curves for S(0) and S(1) show a tendency toward the nonoccurrence of crossing between these two states (in the intermediate region along the C-Cl coordinate), as the basis set size increases. Such tendency is accompanied by a decreasing well depth for the S(1) state. Dynamic electronic correlation (especially at the MR-AQCC level) is also an important factor toward an absence of crossing along the C-Cl coordinate. Further investigations of a possible crossing using gradient driven techniques (at CASSCF and MR-CISD levels) seem to confirm its absence.
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http://dx.doi.org/10.1063/1.2800020DOI Listing
October 2007

An ab initio study of the C2H2-HF, C2H(CH3)-HF and C2(CH3)2-HF hydrogen-bonded complexes.

Spectrochim Acta A Mol Biomol Spectrosc 2006 Feb 19;63(2):383-90. Epub 2006 Jan 19.

Departamento de Química Fundamental, Universidade Federal de Pernambuco (UFPE), Rua Jose Simoes Araujo 352 apto 501, 50739-901, Recife (PE), Brasil.

MP2/6-31++G** and B3LYP/6-31++G** ab initio molecular orbital calculations have been performed in order to obtain molecular geometries, binding energies and vibrational properties of the C2H2-HF, C2H(CH3)-HF and C2(CH3)2-HF H-bonded complexes. As expected, the more pronounced effects on the structural properties of the isolated molecules due to complexation was verified for the C[triple bond]C and H-F bond lengths, which are directly involved in the H-bond formation. These bond distances increased after complexation. BSSE uncorrected B3LYP binding energies are always lower than the corresponding MP2 values. However, the opposite trend has been verified after BSSE correction by the counterpoise method since it is much lower at B3LYP than at MP2 level. The binding energies for these complexes as well as for the HF acid submolecule modes (the HF stretching and vibrational frequency modes) showed an increasing hydrogen-bonding strength with increasing methyl substitution. The splitting in the HF in-plane and out-of-plane bending modes reflects the anisotropy in the hydrogen-bonding interaction with the pi system of the C[triple bond]C bond. The H-F stretching frequency is shifted downward after complexation and it increases with the methyl substitution. The IR intensities of the HF acid submolecule fundamentals are adequately interpreted through the atomic polar tensor of the hydrogen atom using the charge-charge flux-overlap model. The skeletal stretching modes of the Alkyne submolecule are decreased in the complex. The new vibrational modes arising from complexation show several interesting features.
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http://dx.doi.org/10.1016/j.saa.2005.05.024DOI Listing
February 2006

A theoretical study of hydrogen complexes of the XH-pi type between propyne and HF, HCL or HCN.

Spectrochim Acta A Mol Biomol Spectrosc 2006 May 5;64(2):412-7. Epub 2005 Dec 5.

Departamento de Química, Universidade Federal da Paraíba, Rua José Simões Araújo 352 apto 501, Bessa, 58036-300 João Pessoa, PB, Brazil.

The present manuscript reports a systematic investigation of the basis set dependence of some properties of hydrogen-bonded (pi type) complexes formed by propyne and a HX molecule, where X=F, Cl and CN. The calculations have been performed at Hartree-Fock, MP2 and B3LYP levels. Geometries, H-bond energies and vibrational have been considered. The more pronounced effects on the structural parameters of the isolated molecules, as a result of complexation, are verified on RCtriple bondC and HX bond lengths. As compared to double-zeta (6-31G**), triple-zeta (6-311G**) basis set leads to an increase of RCtriple bondC bond distance, at all three computational levels. In the case where diffuse functions are added to both hydrogen and 'heavy' atoms, the effect is more pronounced. The propyne-HX structural parameters are quite similar to the corresponding parameters of acetylene-HX complexes, at all levels. The largest difference is obtained for hydrogen bond distance, RH, with a smaller value for propyne-HX complex, indicating a stronger bond. Concerning the electronic properties, the results yield the following ordering for H-bond energies, DeltaE: propynecdots, three dots, centeredHF>propynecdots, three dots, centeredHCl>propynecdots, three dots, centeredHCN. It is also important to point out that the inclusion of BSSE and zero-point energies (ZPE) corrections cause significant changes on DeltaE. The smaller effect of ZPE is obtained for propynecdots, three dots, centeredHCN at HF/6-311++G** level, while the greatest difference is obtained at MP2/6-31G** level for propynecdots, three dots, centeredHF system. Concerning the IR vibrational it was obtained that larger shift can be associated with stronger hydrogen bonds. The more pronounced effect on the normal modes of the isolated molecule after the complexation is obtained for HX stretching frequency, which is shifted downward.
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http://dx.doi.org/10.1016/j.saa.2005.07.038DOI Listing
May 2006
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